This proposal aims to improve and evaluate Nuclear Medicine procedures in hypertension. Radiorenography with Captopril in the differential diagnosis of renovascular hypertension (RVH) will be evaluated. It is not clear whether Tc99m-DTPA Captopril renography CR or I-131 hippuran CR with gamma camera images are of comparable value. The introduction of Captopril to renography promises to greatly improve the diagnostic accuracy of the test. We propose to study CR using both of these agents in two specific populations of hypertensive patients. Initially, we will direct our efforts towards standardizing CR. Techniques for evaluation of the scintigrams and renographic curves, control of variables such as length of time off medication, dose of captopril, hydration of the patient, timing of the study (same day or sequential days), and other significant variables have not been standardized among centers and need to be addressed. These studies will be complemented by studies in rat models controlling for specific variables. After optimizing these parameters by an initial evaluation of patients with and without renovascular disease, a larger prospective series will be carried out to determine the accuracy of CR. A general population based study is not feasible, but by using two distinctly different populations, reasonable estimates may be obtained. A population rich in patients with renovascular hypertension from the Cornell Medical Center will provide data concerning true positives and false negatives in patients with known RVH. A low prevalence population studied at the Albert Einstein College of Medicine will provide data concerning false positive tests. Since the major difficulty with renography without Captopril is the high false positive rate, these two populations will provide data to determine the role of CR in the differential diagnosis of renovascular disease in the hypertensive patient. It will permit an estimation of the false positive rate, which is the biggest problem encountered today. This study provides a means of standardizing CR, choosing the most suitable isotope for evaluation of renovascular hypertension, and determining the ability of the test to provide information of differential diagnostic value.